A method of continuously casting metal

ABSTRACT

In a continuous casting process the casting is intermittently withdrawn from a stationary horizontal mould by the action of at least one pair of pinch rolls which engage the casting and at least one of the rolls is driven. After each withdrawal phase a push-back force is applied to the casting by the pinch rolls to urge the casting back towards the mould. The push-back force is sufficiently large to allow the casting to contract back towards the mould but it is insufficiently large to cause displacement of the casting at the inlet end of the mould. Apparatus of the invention includes means for driving the pinch rolls in the direction to withdraw the casting from the mould and means by which the drive means is energised after each withdrawal phase to rotate the pinch roll in the opposite direction of rotation to apply a limited push-back force to a casting engageable by the pinch roll. Both pinch rolls are preferably driven in which case they are driven by separate drive means which may be hydraulic motors.

[ A METHOD OF CONTINUOUSLY CASTING METAL [75] Inventors: Peter CharlesDavid Gamble,

Wootton; John Marsh, Putnoe, both of England [73] Assignee: Davy-AshmoreLimited, London,

England [22] Filed: Jan. 18, 1972 [21] Appl. No.: 218,804

[30} Foreign Application Priority Data Jan. 19, 1971 Great Britain2536/71 [52] US. Cl. 164/83, 164/260 [51] Int. Cl B22d 11/02 [58] Fieldof Search 164/82, 83, 260

[56] References Cited UNITED STATES PATENTS 3,354,936 ll/l967 Atkin164/82 3,545,528 12/1970 Chang 3,669,176 l/l972 Krall et a1. 164/83 XFOREIGN PATENTS OR APPLICATIONS 1,087,026 10/1967 Great Britain 164/83June 18, 1974 Primary Examiner-R. Spencer Annear Attorney, Agent, orFirm-Morton, Bernard, Brown, Roberts & Sutherland [57 ABSTRACT In acontinuous casting process the casting is intermittently withdrawn froma stationary horizontal mould by the action of at least one pair ofpinch rolls which engage the casting and at least one of the rolls isdriven. After each withdrawal phase a push-back force is applied to thecasting by the pinch rolls to urge the casting back towards the mould.The push-back force is sufficiently large to allow the casting tocontract back towards the mould but it is insufficiently large to causedisplacement of the casting at the inlet end of the mould.

Apparatus of the invention includes means for driving the pinch rolls inthe direction to withdraw the casting from the mould and means by whichthe drive means is energised after each withdrawal phase to rotate thepinch roll in the opposite direction of rotation to apply a limitedpush-back force to a casting engageable by the pinch roll. Both pinchrolls are preferably driven in which case they are driven by separatedrive means which may be hydraulic motors.

5 Claims, 4 Drawing Figures PATENTEDJUM m 333173313 same ur 2' IDisplacement V Qg laccml I A METHOD OF CONTINUOUSLY CASTING METAL Thisinvention relates to a method of, and apparatus for, the continuouscasting of metals, particularly steel.

Continuous casting consists essentially of allowing molten metal storedin a container, usually in the form of a tundish, to flow through amould and for the metal to be cooled sufficiently in the mould for thecasting leaving the mould to retain the cross sectional shape of themould. The casting is usually withdrawn from the mould by means of oneor more pairs of pinch rolls which engage opposite sides of the castingand at least one roll of each pair is driven.

In the past, vertical continuous casting machines have been used, butthe capital and operating costs of the continuous casting process arereduced if the mould is horizontally aligned and the casting iswithdrawn horizontally. It has also been found that with horizontalcontinuous casting apparatus it is necessary for the mould to be fixedrelative to the tundish and for the inlet end of the mould to be sealedto the outlet of the tundish. Additionally oxidation of the metal streamflowing into the mould is prevented. If a straight through" system oftundish outlet and mould is employed, i.e., a system where the crosssection of the outlet of the tundish and the cross section of the mouldare the same, it has been found that the operation of the apparatus isonly possible by the use of graphite at least at the tundish end of themould. Use of graphite in the mould precludes the casting of metals inwhich graphite is soluble, for example steel. To overcome thisdifficulty it has been proposed to introduce at least one refractoryapertured component which is not soluble in the metal being cast betweenthe outlet of the tundish and the inlet of the mould, with the componenthaving a smaller aperture than the bore of the mould. The component thusprovides an obstruction at the entrance to the mould and the tundish andmould system is then no longer of the straight through type.

To attain high casting speeds, continuous withdrawal from a stationaryhorizontal mould is not possible since any breaks in the solidifyingskin resulting from sticking in the mould do not heal sufficientlyquickly and solidified metal is left behind in the mould. This conditionfrequently leads to rupture of the skin outside the mould and a breakout of molten metal. This difficulty can sometimes be overcome bywithdrawing the casting with an intermittent motion using the pinchrolls. When a pull:pause withdrawal cycle was employed with the abovedescribed non-straight-through system of tundish outlet and mould, itwas found that circumferential hot tears occurred in a cyclic manner onthe surface of the casting. It was discovered that the reason for thisis that during each withdrawal part of the cycle, metal flows into themould and solidifies against the mould wall up to the refractorycomponent. The molten metal also solidifies against the part of thesolid skin which was in contact with the refractory component on theprevious cycle. Between these two solidified portions the thickness ofthe skin is a minimum and is therefore a point of weakness between thetwo parts of the skin. During the pause part of the withdrawal cycle,contraction of the casting causes this point of weakness to open up andform a hot tear.

It has been proposed in British Pat. Specification 1,087,026 to withdrawmetal from a body of molten metal through a continuous casting mould,cooling the withdrawn metal within the mould to effect solidificationthereof as it is being withdrawn, reversing the direction of rotation ofsupporting rollers to reverse the direction of movement of the cooledcasting so as to reintroduce it at least partially into the mould andthen withdrawing the solidified casting further by movement in theoriginal direction. This method of pulling the casting and pushing itback into the mould can only be employed in a straight-through system ofmould and tundish and its use with apparatus having an obstruction atthe mould inlet is not possible. If it was attempted to push the castingback into the mould, the casting would abut against the obstruction andeither force it from its seating with the mould or the thin skinadjacent the obstruction would be forced against the obstruction andcause the skin to be wrinkled thus producing a casting of poor surfacefinish.

According to a first aspect of the present invention in a method ofcontinuously casting metal, the casting is intermittently withdrawn froma stationary horizontal mould by the action of at least one pair ofpinch rolls engaging the casting and with at least one of each pairbeing driven, and after each withdrawal phase a push back force isapplied to the casting by the pinch rolls to urge the casting backtowards the mould. the push back force being sufficiently large to allowthe casting to contract back towards the mould but insufficiently largeto cause displacement of the casting at the inlet end of the mould.

According to a second aspect of the invention, continuous castingapparatus includes a stationary horizontal mould, at least one pair ofpinch rolls engageable with a casting produced in the mould, drive meansfor one of the rolls of each pair and means by which the drive means isintermittently energised to rotate the pinch roll in the direction towithdraw the casting from the mould and means by which the drive meansis energised after each withdrawal phase to rotate the pinch roll in theopposite direction of rotation to apply a limited push-back force to acasting engageable by the pinch roll.

Both pinch rolls of each pair may be driven in which case they aredriven by separate drive means. The drive means for each roll may be ahydraulic motor.

In order that the invention may be more readily understood it will nowbe described, by way of example only, with reference to the accompanyingdrawings in which FIG. 1 is a side elevation, partly in section ofcontinuous casting apparatus,

FIG. 2 is a diagrammatic hydraulic circuit for withdrawal apparatus ofthe continuous casting apparatus, and

FIGS. 3A and 3B are time/displacement graphs at the portion of a castingengaged by a pair of pinch rolls and e at the inlet end of thecontinuous casting mould respectively.

FIG. 1 illustrates the mould tundish arrangement of a horizontalcontinuous casting apparatus. A continuous casting mould, particularlysuitable for casting steel, comprises a tubular upper sleeve Isurrounded by but spaced from a steel jacket 2, but alternatively themould may be made entirely of copper. Liquid coolant is arranged to flowbetween the sleeve and the jacket in order to cool the mould. The sleeve1 defines the mould passage 3 which is arranged with its longitudinalaxis horizontal.

At the inlet end of the mould passage there is provided a refractorybody 4, conveniently of silicon nitride when casting steel. The body isin the form of an apertured plate and its surrounds and abuts againstthe inlet end of the passage with a portion 5 of the body projectinginwardly of the mould passage. A refractory feed tube which constitutesthe outlet nozzle from the tundish 11 is sealed by means of conventionalrefractory cement to the body 4 to prevent leakage between the nozzleand the plate. The mould-tundish is thus not of the straight-throughtype because the plate 4 projects into the mould passage.

A casting produced in the mould passes from the open end of the mouldthrough a secondary cooling zone and is gripped by at least one pair ofpinch rolls (not shown in FIG. 1) located on the side of the secondarycooling zone which is away from the mould. The pinch rolls are thusspaced at some distance from the mould. At least one of the pinch rollsis driven but preferably both rolls of each pair are driven.

The withdrawal of the casting from the mould comprises repeatingwithdrawal cycles each consisting of a pull phase followed by a pushphase during which a limited force is applied to the casting to urge ittowards the mould. During the push phase only movement of the castingequivalent to the contraction of the casting is permitted and thecasting is not forced back into the mould. There is therefore nomovement of the casting at the inlet end of the mould and consequentlythere is no danger of the plate 4 being forced off its seating at theentrance to the mould. Furthermore the thin skin of the castng at theinlet end of the mould is not wrinkled due to movement of the casting atthe inlet end of the mould.

Referring now to FIG. 3, FIG. 3A illustrates a time/- displacement graphfor a portion of the casting situated between the pinch rolls. It can beseen that during the pull phase A the casting is displacedlongitudinally in the direction away from the mould and during the pushback phase B the casting moves back for a short distance towards themould. This push back of the casting is brought about by applying alimited reverse torque to the pinch rolls to allow the casting to moveback to compensate for contraction of the length of casting between themould and the pinch rolls. It can be seen however from FIG. 38 that thecasting is not forced back into the mould because the displacement/timegraph at the inlet end of the mould shows that this part of the castingdoes not move back relative to the mould. During pull phase A thecasting is withdrawn in the direction out of the mould but during thetime interval B it is not displaced back relative to the mould.

A hydraulic circuit for controlling a pair of hydraulic motors driving apair of pinch rolls is illustrated in FIG. 2. A pair of pinch rolls 20,21 are connected to a pair of hydraulic drive motors 22, 23respectively. The motors are connected in series between a pair of fluidlines 24, 25. Alternatively the motors could be connected in parallel.The fluid lines 24, 25 are connected to respective parts on a fluidcontrol valve 26. Three further fluid lines 27, 28 and 29 are connectedto the control valve and the valve is provided with a spool which can bedisplaced by solenoids. The spool of the valve 26 is connectedmechanically to the spool of a by-pass valve 30 which is connectedacross the lines 27, 28. A pump 31 having a relief valve 32 in shuntwith it is connected across the fluid lines 27, 28 and a backing pump 33is connected to supply hydraulic fluid from a reservoir 34 to the inletof the pump 31. A further pump 35 is connected to draw hydraulic liquidfrom the reservoir 34 and supply it through a check valve 36, and a flowcontrol valve 37 to the line 29. A by-pass valve 38 is connected inparallel with the valve 37 and an adjustable pressure relief valve 39 isconnected between the outlet of the pump 35 and the reservoir 34.

In use all the pumps are energised continuously. To apply a withdrawalpull to the casting the spool of the valve 26 is adjusted to theposition in which fluid supplied on the line 27 by the pump 31 is passedto the motors 22 and 23. The by-pass valve 30 is closed and fluidsupplied to the valve 26 by the pump 35 is passed through the valve andreturned to the line 28. The motors are thus rotated in the direction towithdraw the casting from the mould. At the end of the pull phase thevalve 26 is switched so that fluid supplied on the line 29 is suppliedto the motors but in the direction to rotate them in the oppositedirection. The pressure and quantity of fluid supplied to the motors islimited by the valves 39 and 37. The by-pass valve 30 is opened so thatfluid pumped by the pump 3! passes through the by-pass 30 and is notsupplied to the motors.

The by-pass valve 38 may be opened to increase the speed of rotation ofthe motors in the reverse direction when it is necessary to drive adummy bar up to the mould before casting commences.

As an alternative to a hydraulic drive, the pinch rolls could be drivenelectrically. The two drive motors would then be electric motors and thetorque limited push back may be brought about by using eddy currentcouplings and adjusting the current in the coupling circuit. A variableresistor in the power supply to the eddy current coupling circuitenables control of the current to be effected.

We claim:

1. A method of continuously casting metal utilizing a mould having atundish for holding molten metal, a horizontally disposed mould passage,and a feed nozzle through which the molten metal flows to the mouldpassage inlet to pass through and solidify within the mould passage, thefeed nozzle having a cross-section adjacent the mould passage inletsmaller than the crosssection of the mould passage; said methodcomprising the steps of passing molten metal from the tundish throughthe feed nozzle to the mould passage inlet; passing the metal throughthe mould passage while cooling the metal to cause the metal to form acasting; gripping a portion of the casting outside the mould passagebetween at least one pair of pinch rolls with at least one roll beingdriven by a hydraulic motor; intermittently applying hydraulic fluidunder pressure from a source through a first pressure relief valve tothe hydraulic motor to drive at least one roll to withdraw the castingfrom the mould passage in a withdrawal phase of a distance less than thelength of the mould passage; after each withdrawal phase applyinghydraulic fluid under pressure from a source through a second pressurerelief valve to the hydraulic motor to drive at least one roll to applyto the casting a push-back force; and controlling the second pressurerelief valve to limit maximum pressure of the hydraulic fluid to apressure which limits the push-back force to a value less than a maximumvalue which is sufficient to allow the casting to contract in thedirection back toward the mould passage but insufficient to cause theportion of the casting engaging the mould passage inlet to be displacedrelative thereto.

2. A method as claimed in claim 1 in which the rolldriving steps includedriving both rolls of at least one pair of pinch rolls.

3. A method as claimed in claim 1 in which the roll driving stepsinclude driving one roll from a first hydraulic motor and drivinganother roll from a second hydraulic motor.

4. A method as claimed in claim 1 in which the roll driving stepsinclude supplying fluid under pressure from a first pump to thehydraulic motor to drive at least one roll to withdraw the casting andsupplying fluid under pressure from a second pump to the hydraulic motorto drive at least one roll to apply the push-back force to the casting.

5. A method as claimed in claim 4 in which the first roll driving stepincludes placing a control valve in a first valve position, supplyingfluid from the first pump through the control valve to the hydraulicmotor, placing the control valve in a second valve position, andsupplying fluid from the second pump through the control valve to thehydraulic motor.

1. A method of continuously casting metal utilizing a mould having atundish for holding molten metal, a horizontally disposed mould passage,and a feed nozzle through which the molten metal flows to the mouldpassage inlet to pass through and solidify within the mould passage, thefeed nozzle having a cross-section adjacent the mould passage inletsmaller than the cross-section of the mould passage; said methodcomprising the steps of passing molten metal from the tundish throughthe feed nozzle to the mould passage inlet; passing the metal throughthe mould passage while cooling the metal to cause the metal to form acasting; gripping a portion of the casting outside the mould passagebetween at least one pair of pinch rolls with at least one roll beingdriven by a hydraulic motor; intermittently applying hydraulic fluidunder pressure from a source through a first pressure relief valve tothe hydraulic motor to drive at least one roll to withdraw the castingfrom the mould passage in a withdrawal phase of a distance less than thelength of the mould passage; after each withdrawal phase applyinghydraulic fluid under pressure from a source through a second pressurerelief valve to the hydraulic motor to drive at least one roll to applyto the casting a push-back force; and controlling the second pressurerelief valve to limit maximum pressure of the hydraulic fluid to apressure which limits the push-back force to a value less than a maximumvalue which is sufficient to allow the casting to contract in thedirection back toward the mould passage but insufficient to cause theportion of the casting engaging the mould passage inlet to be displacedrelative thereto.
 2. A method as claimed in claim 1 in which theroll-driving steps include driving both rolls of at least one pair ofpinch rolls.
 3. A method as claimed in claim 1 in which the roll drivingsteps include driving one roll from a first hydraulic motor and drivinganother roll from a second hydraulic motor.
 4. A method as claimed inclaim 1 in which The roll driving steps include supplying fluid underpressure from a first pump to the hydraulic motor to drive at least oneroll to withdraw the casting and supplying fluid under pressure from asecond pump to the hydraulic motor to drive at least one roll to applythe push-back force to the casting.
 5. A method as claimed in claim 4 inwhich the first roll driving step includes placing a control valve in afirst valve position, supplying fluid from the first pump through thecontrol valve to the hydraulic motor, placing the control valve in asecond valve position, and supplying fluid from the second pump throughthe control valve to the hydraulic motor.